1. Field of the Invention
The present general inventive concept relates to a device to protect an electronic circuit from a surge voltage and to match an impedance, and more particularly to, an electronic apparatus having a device to protect an electronic circuit from a surge voltage.
2. Description of the Related Art
Generally, a surge voltage is generated by static electricity of a human body as well as by lightning, strong electromagnetism, arc, induction load switching, etc.
Electronic apparatuses such as mobile phones and computers have become smaller and more efficient while an internal voltage of electronic components disposed therein has been lowered.
An internal electric circuit of these electronic apparatuses may be damaged by a static pulse which is generated by contact between the human body and the electronic apparatuses, since a high voltage ranging from hundreds to thousands of volts may be generated by static electricity for a short period of time and may be supplied to the electronic apparatuses.
A varistor is a surge protection device that is disposed between an input line and an output line of the electronic apparatuses and can change resistance according to a supply voltage.
Since the varistor changes its resistance according to the supply voltage, it is widely used to protect main electronic components and circuits from the static electricity generated by the human body. If the varistor receives a surge voltage due to an overvoltage or lightning, the resistance of the varistor drastically decreases creating an instant shunt path for the overvoltage in order to protect the main electronic components and circuits connected in parallel with the varistor from the static electricity and the overvoltage.
That is, the varistor functions as a capacitor if an input voltage is smaller than a predetermined voltage. If the input voltage is larger than the predetermined voltage, the varistor functions as a resistor having a small resistance value.
When the varistor is supplied to a transmission line and comprises a capacitance between terminals (i.e., the input line and the output line), line impedance of the transmission line partially decreases due to the capacitance. As a result, uniformity of the line impedance decreases, thereby deteriorating a signal waveform.
Conventionally, a varistor having a small capacitance is used to minimize the foregoing problem. However, the line impedance is partially decreased even by the small capacitance. Particularly, the signal waveform deteriorates due to the varistor when transmitting a broadband high speed signal.
FIG. 1 illustrates an impedance change when a conventional varistor 2 is used.
As illustrated in FIG. 1, the impedance is changed where a measuring instrument and a transmission line 1 are connected to each other, and is partially lowered where the conventional varistor 2 is connected to the transmission line 1. That is, where the transmission line 1 having an impedance of 100Ω and the conventional varistor 2 having a load of 100Ω are connected to each other, the impedance is lowered to 83 Ω.
The lowered impedance deteriorates signal transmissions and does not satisfy the most recently set signal transmission standards such as the high definition multi-media interface (HDMI).